netdev - Re: [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of stop on timeout

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Message-ID: <a1dc573d-78b0-7137-508d-efcdfa68d936@cogentembedded.com>
Date:   Mon, 29 Jun 2020 11:40:22 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>
Cc:     "REE dirk.behme@...bosch.com" <dirk.behme@...bosch.com>,
        "Shashikant.Suguni@...bosch.com" <Shashikant.Suguni@...bosch.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of
 stop on timeout

Hello!

On 29.06.2020 8:24, Yoshihiro Shimoda wrote:

>>>>> From: Yoshihiro Shimoda, Sent: Tuesday, May 26, 2020 6:47 PM
>>>>>
>>>>> According to the report of [1], this driver is possible to cause
>>>>> the following error in ravb_tx_timeout_work().
>>>>>
>>>>> ravb e6800000.ethernet ethernet: failed to switch device to config mode
>>>>>
>>>>> This error means that the hardware could not change the state
>>>>> from "Operation" to "Configuration" while some tx queue is operating.
>>>>> After that, ravb_config() in ravb_dmac_init() will fail, and then
>>>>> any descriptors will be not allocaled anymore so that NULL porinter
>>>>> dereference happens after that on ravb_start_xmit().
>>>>>
>>>>> Such a case is possible to be caused because this driver supports
>>>>> two queues (NC and BE) and the ravb_stop_dma() is possible to return
>>>>> without any stopping process if TCCR or CSR register indicates
>>>>> the hardware is operating for TX.
>>>>>
>>>>> To fix the issue, just try to wake the subqueue on
>>>>> ravb_tx_timeout_work() if the descriptors are not full instead
>>>>> of stop all transfers (all queues of TX and RX).
>>>>>
>>>>> [1]
>>>>> https://lore.kernel.org/linux-renesas-soc/20200518045452.2390-1-dirk.behme@de.bosch.com/
>>>>>
>>>>> Reported-by: Dirk Behme <dirk.behme@...bosch.com>
>>>>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>>>> ---
>>>>>    I'm guessing that this issue is possible to happen if:
>>>>>    - ravb_start_xmit() calls netif_stop_subqueue(), and
>>>>>    - ravb_poll() will not be called with some reason, and
>>>>>    - netif_wake_subqueue() will be not called, and then
>>>>>    - dev_watchdog() in net/sched/sch_generic.c calls ndo_tx_timeout().
>>>>>
>>>>>    However, unfortunately, I didn't reproduce the issue yet.
>>>>>    To be honest, I'm also guessing other queues (SR) of this hardware
>>>>>    which out-of tree driver manages are possible to reproduce this issue,
>>>>>    but I didn't try such environment for now...
>>>>>
>>>>>    So, I marked RFC on this patch now.
>>>>
>>>> I'm afraid, but do you have any comments about this patch?
>>>
>>>      I agree that we should now reset only the stuck queue, not both but I
>>> doubt your solution is good enough. Let me have another look...
>>
>> Thank you for your comment! I hope this solution is good enough...
> 
> I'm sorry again and again. But, do you have any time to look this patch?

    Yes, in the sense of reviewing -- I don't consider it complete. And no, in 
the sense of looking into the issue myself... Can we do a per-queue tear-down
and re-init (not necessarily all in 1 patch)?

> Best regards,
> Yoshihiro Shimoda

MBR, Sergei